A multidisciplinary approach involving behavioral, electroretinographic and a wide variety of neuroanatomical techniques will be used to continue our study of the synaptic organization of the goldfish retina. Synaptic Plasticity of Bipolar Cell Terminals - Synaptic terminals of mixed rod/cone bipolar cells undergo morphological changes with light and dark adaptation. Electron microscopy will be used to study the time course, circadian properties, retinal regional variation, pharmacological bases, and synaptic input to these bipolar cell terminals during changes in adaptation. Differences in the electrophysiological and pharmacological properties of the synaptic terminals will be studied in the retinal slice preparation using whole-cell recording techniques. Activity dependent changes in synaptic morphology are well documented in mammalian hippocampus. The goldfish retina provides an excellent preparation to study analogous events in the vertebrate retina. Dopamine Depletion Increases Perceived Brightness - Dopamine depletion by intravitreal injection of 6-hydroxydopamine appears to increase perceived brightness in goldfish. The hypothesis is that dopamine is involved in controlling the balance of rod/cone output in the outer retina and can act in a paracrine (at a distance) mode. During the time course of dopamine interplexiform cell absence (2-6 weeks) and appearance at the marginal zone (6-24 weeks) properties of the dopamine-depleted eye will be compared to control: brightness perception as determined by the dorsal light reflex (a behavioral tilt to different intensities of light to the two eyes), increment thresholds of the ERG a-wave and b-wave, distribution of dopamine D1 and D2 receptors by binding autoradiography, effect on horizontal cell spinules (assay for intact dopamine in light- adapted retina). The loss of a single neuron type (dopamine IPC) of very low frequency has a marked behavioral effect indicative of an important role in light and dark adaptation. Dopamine is highly conserved in vertebrate retinae. These studies will provide important information on retinal dopamine function. Synaptic Organization of Cone Bipolar Cells in the inner plexiform layer is virtually unknown. Combined Golgi impregnation and postembedding immunocytochemistry of GABA and glycine antisera will be used at the EM level to study the differential organization of individual stratum for multistratified cone bipolar cells, particularly those whose strata span both sublaminae (ON and OFF layers) of the IPL.